I have a preference for longnecks too, as that is what I have the most number of bottles.
As for numbers 6 members would work for 2 longnecks per member per case. 12 members would work best with 1 longneck per member per case as I'd image two cases each would get a bit hard logistically.
For a central point, I'd imagine it would work best to base it nearest the majority of the members. ie. If most are in Newcastle then someone in Newcastle etc.
Beers,
Doc